DictOn is an app that makes word-checking faster than ever before! You simply set a keyboard shortcut for DictOn (or use the default ctrl+space ) and then whenever you use it, it will display DictOn's window on top of other programs the same way Spotlight Search displays on macOS. Type in the word, click enter, voilà!
To install a new dictionary, open the settings by clicking the gear icon, then drag and drop .dict file into an appropriate field.